Dan Vanderkam

TypeScript is a superset of JavaScript in a syntactic sense: so long as your JavaScript program doesn’t have any syntax errors then it is also a TypeScript program.

One of the goals of TypeScript’s type system is to detect code that will throw an exception at runtime, without having to run your code.

While TypeScript can catch errors even if you don’t provide type annotations, it’s able to do a much more thorough job if you do.